[j-nsp] Finding drops

Saku Ytti saku at ytti.fi
Tue Jan 22 04:49:09 EST 2019

On Mon, 21 Jan 2019 at 22:09, Jason Lixfeld <jason-jnsp at lixfeld.ca> wrote:

> I’ve distilled the test down to generating 100 million 64 byte (UDP) packets to the destination, but the counters on et-0/0/2 read as though they’ve only received about 76.6% of those packets.

This caught my eye.

84B / 64B = 76.19% - awfully close to what you're seeing.

What are you actually doing? How are measuring rates?

JunOS SNMP and 'show int' measures _l3 speed_, which is 20/84 = 23.8%.
So worst case you see 23.8Gbps out of 100Gbps interface, when it's
fully congested, because you're measuring wrong thing.

SNMP standard says L2 rate, which is 76.19Gbps out of 100Gbps, which
is also measuring wrong thing. So everyone is looking at stats, which
are wrong, unless they post-process and approximate the bps to be bps
+ (pps* overhead).

You actually want to measure true L1 rate (preamble 1, sfd 7, dmac 6,
smac 6, etype 2, payload 46, crc 4, ifg 12).

MX204 is single Eagle trio, certainly can't do wire-rate on all ports,
but can do in one port.


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